In the human knee, the anterior cruciate ligament (i.e., the ACL) extends between the top end of the tibia and the bottom end of the femur. This ligament plays an important role in providing both static and dynamic stability to the knee. Often, the ACL is ruptured or torn as the result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee.
For example, the ACL may be reconstructed by replacing the damaged ACL with a synthetic or harvested graft ligament. More particularly, with such a procedure, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways well known in the art so that the graft ligament thereafter extends between the tibia and the femur in substantially the same way, and with substantially the same function, as the original ACL.
In some circumstances, a graft ligament harvested from the body may include a bone block connected to one or both of its ends. For example, a portion of a patella tendon, with a portion of the patella still attached, may be harvested from the patient so as to provide the graft ligament. The graft ligament's bone block (i.e., the patella block) can facilitate integration of the graft ligament with the patient's host bone, due to the rapid integration of bone with bone.
In other circumstances, a graft ligament harvested from the body may consist entirely of soft tissue. For example, a portion of the hamstring tendon may be harvested from the patient so as to provide the graft ligament. In this case, only the soft tissue is available to integrate with the host bone.
In one well-known procedure, the graft ligament is placed in the bone tunnel and then fixed in place using a headless orthopedic screw, generally known as an “interference” (or “Kurosaka”) screw. More particularly, with this procedure, the graft ligament is placed in the bone tunnel and then an interference screw is advanced into the bone tunnel so that the screw extends parallel to the bone tunnel and simultaneously engages both the graft ligament and the host bone. The interference screw essentially drives the graft ligament laterally, into engagement with the opposite side of the bone tunnel, whereby to secure the graft ligament to the host bone.
Interference screws work well in many circumstances. Unfortunately, however, interference screws do not work perfectly in all clinical situations. For example, interference screws can have limited effectiveness where bone quality is poor. This can be particularly true in the tibia. In fact, in some circumstances, the bone quality in the tibia can be sufficiently poor that a surgeon will avoid the use of an interference screw altogether and uses some alternative form of ligament fixation. Unfortunately, however, such alternative forms of ligament fixation generally suffer from significant deficiencies of their own.
In addition to the foregoing, other objects frequently need to be attached to bone as well. For example, in the area of fracture fixation, bone fragments need to be re-attached to bone. Current attachment techniques typically rely on the use of bone screws and the like to effect re-attachment. However, bone screws typically only provide a single point of purchase with the bone and can provide less than optimal stability, frequently requiring the use of additional screws, etc.